1. Field of the Invention
The present invention generally relates to an optical system for a micro analyzing system. More specifically, the invention relates to an optical system for a micro analyzing system used for optically analyzing a very small amount of sample in the field of chemistry, such as biochemistry or analytical chemistry, medicine or the like.
2. Description of the Prior Art
In recent years, there has been developed a micro analyzing system wherein a micro space, which functions as a flow passage, a reacting portion, a separating portion or a detecting portion, is formed in a microchip of a glass or plastic to rapidly process a very small amount of sample in the microchip. FIG. 9 shows an example of a microchip 41 for electrophoresis, to which a conventional optical system 48 for a micro analyzing system is applied. As shown in FIG. 9, the microchip 41 has a plate member 42 in which a sample passage 45 and a separation passage 46 are formed so as to cross each other. In the sample passage 45 and separation passage 46, a sample separating medium is previously filled. The microchip 41 is designed to separate and identify a sample by the following process. First, a sample is injected from one end portion of the sample passage 45, and a voltage is applied to both ends of the sample passage 45 to move the sample due to electrophoresis until the front end of the sample passes through a passage crossing portion 47. Then, a voltage is applied to both ends of the separation passage 46 to feed a very small amount of sample, which is positioned at the passage crossing portion 47, into the separation passage 46 to start the separation of the sample. As shown in FIGS. 10 and 11, the sample moving in the separation passage 46 due to electrophoresis has different electrophoretic speeds in accordance with a difference in molecular weight or the like, and is separated into a plurality of bands (a group of materials) 43 until it reaches the optical system 48. The sample (band 43) reaching the optical system 48 is irradiated with light beams from an optical fiber 54, and fluorescence emitted from the fluorescent label of the sample is detected by a detecting means (e.g., a light receiving element) 55 to analyze the sample (see, e.g., Japanese Patent Laid-Open Nos. 11-64278 and 2002-214194).
In such a conventional optical system 48 for the micro analyzing system which is applied to the microchip 41, light beams emitted from the tip of the optical fiber 54 connected to a light source (not shown) are condensed by a cylindrical lens 49 having a spherical lens surface viewed in directions perpendicular to the plane of FIGS. 10 and 11, and the sample (band 43) moving in the separation passage 46 due to electrophoresis is irradiated with the light beams condensed by the spherically cylindrical lens 49, so that fluorescence emitted from the sample is detected by the detecting means 55 (see S. Camou et al., “Design of 2-D optical lens on a PDMS micro-chip to improve fluorescence spectroscopy using integrated optical fibers”, Optical MEMS 2001, 25-28, September 2001, pp. 133-134).
However, in the optical system 48 for the micro analyzing system shown in FIG. 10, the width (the width in directions in which the sample moves due to electrophoresis) of light beams obtained by condensing divergent beams, which are emitted from the optical fiber having a predetermined core diameter, by means of the spherically cylindrical lens 49 is large. Therefore, if the distance between adjacent two of the bands 43 is decreased as shown in FIG. 11, there are some cases where adjacent two or more of the bands 43 in the moving direction due to electrophoresis may be simultaneously irradiated with light beams, so that fluorescence simultaneously emitted from the plurality of bands 43 may be detected by the detecting means 55. In addition, there are some cases where fluorescence from a sample other than a target sample may be simultaneously picked up, so that the precise of analysis is not always satisfied. Moreover, in order to ensure the precision of analysis, if the distance between adjacent two of bands is increased so that only a target sample (band) is irradiated with measuring beams, the time required to carry out measurement increases. Thus, it is desired for research workers in the field of chemistry, such as biochemistry or analytical chemistry, medicine or the like to obtain an optical system for a micro analyzing system capable of more precisely and rapidly analyzing a sample.